This invention relates to a process for diagnosing defects in an exhaust gas recirculation device of an internal-combustion engine system having an engine timing gear with a knock control.
Known processes for diagnosing defects of exhaust gas recirculation devices in internal-combustion engine systems are based on the use of different sensors in the intake pipe area or in the area of an exhaust gas recirculation pipe, such as the pressure, temperature or pollutant sensing system. See, for example, German Patent Documents DE 38 28 477 A1, DE 41 35 190 A1, DE 42 12 636 A1, DE 42 24 219 A1 and DE 43 26 351 A1. In addition, in the process described in German Patent Document DE 42 12 636 A1, in order to keep the engine torque constant during the diagnosis, a firing point adjustment is carried out according to a detected change of the engine running condition, for diagnostic purposes, each time the exhaust gas recirculation valve is switched from an opened position into a closed position or vice versa.
Another process for diagnosing defects of an exhaust gas recirculation system is disclosed in European Patent Document EP 0 219 202 A2. In that arrangement the operability of the exhaust gas recirculation system is detected without ally special sensors, by taking advantage of the fact that during steady-state operating condition, the exhaust gas recirculation system is switched off. Thus, the fuel/air ratio is observed during steady state operation, specifically the integral proportion of the controlling device output signal of a corresponding fuel/air mixture control. When the change of this integral proportion is less than a given value, this is interpreted as a defect in the exhaust gas recirculation device.
On the other hand, internal-combustion engine systems are known which have an engine timing gear with a knock control. As an example, reference is made to German Patent Document DE 39 34 017 C2 and the literature cited there.
The object of the present invention is to provide a process for diagnosing defects of an exhaust gas recirculation device for an internal-combustion engine having an engine timing gear with a knock control, which process can detect defects in the exhaust gas recirculation system in a simple manner, without any special sensor system.
This object is achieved according to the invention, by utilizing the existing knock control of the engine timing gear, as well as the fact that in the case of an activated and properly functioning exhaust gas recirculation system, the knock limit shifts when the exhaust gas recirculation rate is reduced. In contrast, if the exhaust gas recirculation system is not intact, the knock limit does not change as a result of the adjustment of the exhaust gas recirculation device in the direction of a reduced exhaust gas recirculation rate.
A motor which is operating with exhaust gas recirculation has a different knock limit than one which operates without exhaust recirculation. Specifically the knock limit of the motor with recirculation is advanced by several degrees. (Typical examples are 20.degree. and 24.degree. before OT, respectively.) Thus, the process according to the invention is performed only when it is determined that the vehicle is at a steady state, with the exhaust gas recirculation system operating--that is, exhaust gas is being recirculated. When these conditions exist the recirculation system is activated to reduce the amount of exhaust gas which is recirculated and the knocking behavior of the engine is observed. If it is then necessary to retard the firing point in order to avoid knocking, it is concluded that the recirculation system is functioning normally. If, on the other hand, the actuation of the system to reduce the amount of exhaust gas recirculation does not cause a shift (or causes a minimal shift of, for example, 2.degree. or less) in the knock limit--thus necessitating a retardation of the firing point--then it is concluded that the system is defective.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.